PREPARATION AND REACTIONS OF ORGANORUTHENIUM(IV) COMPLEXES

Oxidative addition of Ru(eta-5-C5R5)L2X (R = H or CH3; L = CO or Ph3P; X = Cl or Br) or [Ru(eta-5-C5Me5)Cl2]2 with allylic halides gives new series of allylruthenium (IV) complexes, Ru(eta-5-C5R5)(eta-3-CH2CHR'CH2)X2. The structure of the representative one (R = CH3; X = Br) was determined unequivocally by single crystal X-ray analysis and H-1-and C-13-NMR spectroscopy. These allylruthenium (IV) complexes and the known Ru (1-3:6-7:10-12-eta-C12H18) Cl2 were successfully methylated by means of CH3MgX or equimolar quantity of CH3Li to yield thermally stable allylhalomethylruthenium (IV) complexes. These alkyl complexes induces selective reductive elimination accompanying the carbon-carbon bond formation between methyl and allyl ligands in the presence of CO, t-BuNC, etc., at elevated temperatures. Alkylation with an excess CH3Li or Me3Al furnished purely organometallic dimethyl complexes, Ru(eta-5-C5R5)(eta-3-C3H5)(CH3)2, which were converted to Ru(C5R5)(eta-3-CH2CHCH-CH3)L (L = CO or t-BuNC) upon heating with evolution of methane. Alternatively, extremely facile beta-hydride elimination followed by the C-H bond-forming reductive elimination took place even below -20-degrees-C, when Et3Al or BrMg (CH2)4MgBr were employed as alkylating reagents. The reactivity of the Ru(IV)-C bonds are, therefore, in the following order, beta-elimination > reductive elimination to form C-H bonds >> reductive elimination to form C-C bonds. It is noteworthy that the insertion of CO, t-BuNC, or alkenes into the Ru(IV)-C bonds was never observed at all. On the other hand, cationic ruthenium active species, [Ru(C5R5)(eta-4-butadiene)]+ induces oxidative cyclization with the second molecule of butadiene to give stoichiometric and catalytic linear di- and trimerization (R = H) or cyclodimerization (R = CH3) of butadiene.